1. Field of the Invention
The present invention relates to a mobile communication terminal and, more particularly, to a technology of improving voice call success ratio in a hybrid phone supporting voice, low-rate and high-rate data communications.
2. Description of Related Art
A hybrid phone refers to a mobile communication terminal which allows a user to use voice and low-rate data communication services over an IS-95/1x network and to use a high-rate data communication service over a High Data Rate (HDR) network by combining IS-95/1x technology with HDR technology.
The HDR technology refers to a packet wireless data transmission technology developed using CDMA technology by Qualcomm Inc., which allows mega class high-speed data transmission, e.g., a maximum transmission speed of 2.547 Mbps within a CDMA cell site. HDR offers a transmission speed as fast as 16 times the maximum transmission speed of 153.6 Kbps on a forward channel of the IS-95/1x system and also provides a data transmission capacity as much as 5 times that of the IS-95/1x system.
HDR offers a user with a hybrid phone voice and high-speed wireless data services by means of an HDR access point function provided independently from a Base Transceiver Station (BTS) or an HDR access point function incorporated in the BTS.
FIG. 1 is a block diagram of a mobile communication system according to the prior art. A mobile communication system 100 includes an IS-95/1x network module 110 processing voice communication and an HDR network module 120 processing high-speed data communication. The IS-95/1x network module 110 includes an IS-95/1x BTS 111, a Base Station Controller (BSC) 112, a Mobile Switching Center (MSC) 113, and an InterWorking Function (IWF) 116. The HDR network module 120 includes an HDR access point 121, a BSC 112, a Packet Control Function (PCF) 123, a Packet Data Serving Node (PDSN) 124, and a Home Agent (HA) 125.
The IS-95/1x BTS 111 establishes a wireless connection with a hybrid phone 200 in an IS-95/1x mode, and acts to convert signal formats to be suitable for wireless and wireline links. The BSC 112 handles allocation of radio channels, receives measurements from the hybrid phone, and controls handovers from BTS to BTS. The MSC 113 is a sophisticated telephone exchange which provides circuit-switched calling and mobility management to the hybrid phone roaming within the area that it serves. The IWF 116 is used to provide circuit switched data services when connecting a mobile communication network to the Internet.
The HDR access point 121 establishes a wireless connection with the hybrid phone 200 for high-speed data communication and controls data transfer with the hybrid phone 200. The HDR access point 121 may be provided separately from or incorporated in the IS-95/1x BTS 111 of the IS-95/1x network module 110. The BSC 112, which is also used for the IS-95/1x network module 110, performs a process required for operation of the HDR access point 121. The PCF 123 controls the transmission of packets between the HDR access point 121 and the PDSN 124. The PDSN 124 is responsible for the establishment, maintenance and termination of a PPP (Point-to-Point Protocol) session towards hybrid phones. The HA 125 performs mobile IP authentication for packet data services in connection with the PDSN 124.
The hybrid phone 200 detects signal strengths of base stations over a pilot channel upon initial power-on, makes synchronization with a base station having the largest signal strength over a sync channel, and requests hybrid phone location registration and subscriber authentication from the IS-95/1x BTS 111. The hybrid phone 200 performs a channel acquisition process upon completion of successful location registration and subscriber authentication.
The hybrid phone 200 acquires a channel for voice and low-rate data communication modes using the IS-95/1x technology and acquires a channel for a high-rate data communication mode by making reference to a Preferred Roaming List (PRL) file containing a channel list of each communication mode stored in a memory upon manufacture of the hybrid phone 200.
FIG. 2 is a flow chart of a conventional channel acquisition process in a hybrid phone. Upon power-on, a hybrid phone attempts to acquire a channel for a first communication mode supporting voice and low-rate data communications (operations S401, S402). The hybrid phone switches the first communication mode to an idle state after acquiring the channel (operations S403, S404). Subsequently, the hybrid phone attempts to acquire a channel for a second communication mode supporting high-rate date communication (operation S405). The hybrid phone determines whether or not the channel for the second communication mode has been acquired (operation S406). If the channel is determined to have been acquired, the second communication mode is switched to an idle state (operation S407). The hybrid phone reattempts to acquire a channel for the first communication mode. If the channel is determined to have been acquired, operations S402 to S406 are repeated to attempt to acquire a channel for the second communication mode. Next, the hybrid phone determines whether or not a power-off signal is input (operation S408). If the power-off signal is not input, operation S402 is performed to attempt to acquire a channel for the first communication mode. If the power-off signal is input, the channel acquisition process is ended.
As described above, the hybrid phone is configured to acquire channels for each communication mode so that a user can use both voice/low-rate data communication services and a high-rate data communication service. That is, the hybrid phone acquires a channel for the first communication mode for voice and low-rate data communications and a channel for the second communication mode for high-rate data communication, and periodically monitors slots assigned for the first and second communication modes to perform a paging process.
However, when the hybrid phone is located in an area in which data communication services do not work well, e.g., in an area in which channels for voice and low-rate data communication modes can be acquired but channels for a high-rate data communication mode cannot be acquired, the hybrid phone continuously attempts to acquire channels for the high-rate data communication mode while the voice and low-rate data communication mode is maintained in an idle state. In this case, it is difficult for the hybrid phone to receive voice calls normally. Accordingly, there is a problem in that the hybrid phone has a lower voice call success ratio than a mobile phone supporting only voice and low-rate data communication services.